This invention relates generally to electrically conductive materials and, more particularly, to high-temperature electrically conductive materials that are curable at low temperatures.
Conductive adhesives and pastes are well known. Generally, these materials include an organic polymer binder material filled with varying amounts of different types of conductive metals. U.S. Pat. No. 6,156,237 discloses an example of one such material. Specifically, this patent describes a conductive paste that includes an organic binder, an inorganic glass or ceramic powder, a conductive metal, and a mono-ol compound.
One problem of organic-based conductive materials is their tendency to exhibit fairly high curing temperatures and relatively low operating temperatures. The material of the ""237 patent, like other materials of this type, requires a high curing temperature of about 850xc2x0 C. Even the best performing materials of this type, however, generally have operating temperatures that do not exceed 250xc2x0 C. Also, materials of this type, while electrically conductive, generally have fairly high resistance values in the range of about 30 xcexa9/cm to about 50 xcexa9/cm. Furthermore, these materials often lack good adhesion to various surfaces, especially ceramics, and many lose their electrically conductive and adhesive properties over time.
It should be noted that the curing temperature for a material is a temperature necessary to transform a green material, or uncured material, into a material having a desired set of characteristics and properties. The operating temperature refers to an upper temperature limit below which a given material maintains a particular property or characteristic. For example, an operating temperature may be marked by a temperature where a material melts or begins to soften to a point where desired structural characteristics of the material are degraded below a predetermined level. In addition to structural properties, the operating temperature may be related to any temperature-dependent characteristic of a material.
Another category of electrically conductive materials, namely aluminum-filled phosphate coatings, is also known. These materials, however, are available only as thin coatings. Further, they require high temperature curing (about 650xc2x0 C.-about 850xc2x0 C.) and need bead peaning to develop electrical conductivity.
The present invention solves one or more of the problems associated with the methods and materials of the prior art and provides a high-temperature, electrically conductive material having a low curing temperature and low resistance.
One aspect of the present invention includes a method of making an electrically conductive material. This method includes supplying a phosphate binder and adding Ag particles to the binder to obtain a mixture including Ag in an amount of between about 8% to about 70% by volume. The mixture is dried for a predetermined length of time. The dried mixture is then cured.
A second aspect of the present invention includes an electrically conductive material. This material includes a phosphate glass having a generic chemical formula of AB(PO4), where A is selected from Al, Fe, and oxides thereof, and where B is selected from Cr, Mo, and oxides thereof. Ag particles are dispersed within the phosphate glass in an amount of between about 8% to about 70% by volume.